Bath and process for chemical metal plating

ABSTRACT

A BATH FOR PLATING A MATERIAL WITH A TRANSITION METAL SELECTED FROM THE CLASS CONSISTING OF NICKEL, COBALT, IRON AND CHROMIUM BY CHEMICAL DEPOSITION WHICHOMPRISES AN AQUEOUS SOLUTION OF A COORDINATION COMPOUND OF THE TRANSITION METAL WITH A SATURATED SHORT CHAIN CARBOXYLIC ACID HAVING 1-CARBON ATOMS AND THE HYDROXY DERIVATIVES OF THE ACID, A LIGAND COMPLEXING AGENT SELECTED FROM THE GROUP OF PYROPHOSPHORIC ACID, ASCORBIC ACID, ERYTHORBIC ACID, THE WATER-SOLUBLE SALTS THEREOF AND THEIR MIXTURES, AND A TRANSITION METAL REDUCING AGENT. THE BATH HAS A PH RANGING FROM 1-14 AND CONTAINS LESS THAN ABOUT 3400 P.P.M. OF CHLORIDE AND/OR SULFATE ANIONS. WHEN THE MATERIAL BEING PLATED IS BISMUTH, CADMIUM, TIN, LEAD OR ZINC, THE BATH CONTAINS LESS THAN 1000 P.P.M. OF THESE ANIONS.

3,627,545 BATH AND PROCESS FOR CHEMICAL METAL PLATING Glenn 0. Mallory, Jr., Inglewood, and Donald W.

Baudrand, Temple City, Calif., assignors to Allied Research Products, Inc., Baltimore, Md.

No Drawing. Continuation of abandoned application Ser.

No. 833,163, June 13, 1969, which is a continuationin part of application Ser. No. 804,369, Feb. 26, 1969, which is a continuation-in-part of abandoned application Ser. No. 661,218, Aug. 17, 1967, which in turn is a continuation-in-part of abandoned application Ser. No. 468,921, July 1, 1965. This application June 5, 1970, Ser. No. 41,784.

Int. Cl. C23c 3/02 US. Cl. 106-1 5 Claims ABSTRACT OF THE DISCLOSURE A bath for plating a material with a transition metal selected from the class consisting of nickel, cobalt, iron and chromium by chemical deposition which comprises an aqueous solution of a coordination compound of the transition metal with a saturated short chain carboxylic acid having l-6 carbon atoms and the hydroxy derivatives of the acid, a ligand complexing agent selected from the group of pyrophosphoric acid, ascorbic acid, erythorbic acid, the water-soluble salts thereof and their mixtures, and a transition metal reducing agent. The bath has a pH ranging from 1-14 and contains less than about 3400 ppm. of chloride and/or sulfate anions. When the material being plated is bismuth, cadmium, tin, lead or zinc, the bath contains less than 1000 ppm. of these anions.

This is a continuation of application Ser. No. 833,163, filed June 13, 1969, now abandoned, which in turn is a continuation-in-part of application Ser. No. 804,369, filed Feb. 26, 1969, which in turn is a continuation of Ser. No. 661,218, filed Aug. 17, 1967, now abandoned, which in turn is a continuation-in-part of application Ser. No. 468,921, filed July 1, 1965, now abandoned.

This invention relates to plating of a material by chemical deposition and, in particular, to the electroless plating of a metal selected from the group consisting of nickel, cobalt, iron, chromium and their mixtures on the surface of the material from an aqueous plating bath comprising a water-soluble source of the metal, a ligand complexing agent and a reducing agent.

The water soluble source of the metal is a coordination compound of the metal with a saturated short chain carboxylic acid having 1-6 carbon atoms and hydroxy derivatives of said acids. Representative monocarboxylic acids suitable for use in the present invention include formic and acetic acids; representative dicarboxylic acids include oxalic, malonic and succinic aids; suitable hydroxy arboxylic acids include glycolic, citric, lactic and gluconic acid.

The ligand complexing agent employed in the bath of this invention is one of the following compounds; pyrophosphoric acid, ascorbic acid, erythorbic acid, the water-soluble salts thereof and their mixtures.

Suitable reducing agents include hypophosphorous acid, an alkali, alkali metal or alkaline earth metal hypophosphite such as ammonium, sodium, potassium, lithium, calcium, magnesium, strontium, barium, etc. hypophosphites or various combinations thereof; water-soluble boranes such as dimethylamine borane and morpholine borane and hydrazine hydrates.

A buffering agent such as a weak acid or base can be employed to maintain the pH of the plating bath between 1 to 14 and the choice of the buffering agent will United States Patent 0" 'ice depend upon whether an alkaline or acidic plating bath is to be employed. Representative buffering agents include sodium or potassium hydroxide and citric acid. For example, in a hypophosphite type bath, where the hardness of the metal plate is important, an acid bath is used since the greater amount of phosphorus deposited with the metal in an acid bath produces a substantially harder plate than an alkaline bath. Where the speed of plating is paramount, an alkaline bath is used. The higher plating rate of an alkaline bath prevents the deposition of amounts of phosphorus comparable to acid baths and the hardness of the plate is diminished.

Still other compounds can be included in the aqueous metal plating bath of this invention such as accelerating agents which include water soluble inorganic and organic carbonates. These accelerating agents also can function as secondary buffering agents and to some extent as complexing agents. Representative accelerating agents include ammonium, potassium, lithium, sodium and choline carbonate.

The aqueous plating bath of this invention thus comprises as a water-soluble source of the metal to be plated a coordination compound of nickel, cobalt, iron and chromium with a short chain carboxylic acid having 1-6 carbon atoms or the hydroxy derivatives thereof in amounts ranging from about 1-80 grams/liter; a ligand complexing agent selected from the group consisting of pyrophosphoric acid, ascorbic acid, erythorbic acid, the watersoluble salts thereof and their mixtures in amounts rang ing from about 1-60 grams/liter; and a reducing agent in amounts ranging from about 1-100 grams/liter. The bath can also include a buffering agent in amounts sufficient to maintain the pH between 1-14 and generally amounts ranging from about 01-100 grams/liter will be sufficient to achieve this purpose. It will be recognized though that less or even greater amounts can be employed. If an accelerating agent is employed it can be added to the bath in amounts ranging from about 7.5- grams/ liter.

In one embodiment of this invention the substrate plated with one or more of the above metals from a bath as described herein can be a substrate which the art recognizes as catalytic to the plating operation or one which can be plated through galvanic initiation or one which is rendered catalytic by sensitizing or pretreating the same. Thus the substrate can include such materials as iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, gold, copper, silver, beryllium, germanium, aluminum, carbon, vanadium, molybdenum, tungsten, chromium, selenium, titanium, uranium and plastics. In plating such a substrate the content of chloride and/or sulfate ions in the. bath, in accordance with the present invention, is no greater than about 3400 ppm.

In another embodiment of the present invention the substrate plated with one or more of the above metals from a bath as described herein can be a non-catalytic substrate selected from the group consisting of bismuth, cadmium, tin, lead, zinc and their combinations. Heretofore it has been recognized in such publications as British Pat. 821,763 and US. Pat. 2,935,425 and 2,766,138 that conventional electroless plating solutions have been incapable of depositing plating metals on these materials. In plating such a substrate, the content of chloride and/ or sulfate ions in the bath in accordance with the present invention is no greater than about 1000 ppm.

It has been known heretofore to produce electroless plating baths from a metal such as nickel, cobalt, iron or chromium in the form of its chloride, sulfate, formate, acetate, sulfonate, gluconate, succinate, malonate or citrate and to include in such a bath as a complexing agent various carboxylic and hydroxycarboxylic acids such as citric, oxalic, tartaric, adipic, succinic, hydro- EXAMPLE 5 acetic, hydroxysuccmic, gluconic, hydroxymalonic and Preferred Range the1r water-soluble salts; various amines such as ethylene diamine, diethylene triamine, ethylene diamine tetraa eg-p- 12 7 h h h Cobaltous citrate, pp. 25 10-60 acetic acid, and \anous s ort am a 1p a 1c ammocar- 203mm pyrophlosphlate, g8 80 5 0 r i mine- 0 ium hypop osp ite,g.p. b xyilc such as a.ammop,oplo.n c acld a Sodium oarbonate,g.p.l 25 1040 propionic acid, and warninobutyric acid. Such disclosures Sodium hydroxide, 5 1 1Q can be found, for instance, in US. Pats. 2,871,142; g 2 3 2 15 2,935,425; 2,942,990; 3,041,198; 3,096,182; 3,121,644; 3,148,072; 3,178,311 and 3,198,659,

The prior art has not recognized, however, that the EXAMPLE 6 liquid complexing agents of the present invention produce Preferred Range a bath exhibiting excellent stabdity characteristics when Nickelglrywmmgpl 30 IMO the bath is limited to a chloride and/or sulfate 1011 conliprphol ge borane, g-p. 3 7 1-6 centration of less than about 3400 ppm. and in the situa- ;f{ ??f ;-R;;- 1:11:13: 2 1 tion when a noncatalytic substrate of a metal selected p u 100 60-200 from the group consisting of bismuth, cadmium, tin, lead, zinc or their combinations is to be plated, the chloride and/ or sulfate ion concentration is less than about 1000 ppm Similar baths are prepared using as the source of the It has been found that with plating baths including a 2,0 nickel, cobalt, iron, chromium or their mixtures the chloride or sulfate ion concentration greater than the formates, acetates, oxalates, malonates, succinates, maximum values reported above, the stability of the bath glycolates, citrates, lactates and gluconates thereof. Adis appreciably and deleteriously affected which in turn ditionally, such baths can employ hypophosphorous acid disadvantageously affects the plating rate and/or the or such hypophosphites as ammonium, lithium, calcium, quality of the plate deposited on a catalytic surface, notmagnesium and barium as the reducing agent. withstanding the particular conventional complexing agent In employing the above baths, conventional plating employed in combination therewith, In contrast, the procedures are implemented. Thus, the temperature of present invention overcomes the instability of such platthe bath is adjusted to a suitable level ranging generally ing baths by limiting the maximum concentration of from ambient temperature to the boiling point of the sulfate and/ or chloride ions therein and by incorporatbath. The material or article to be plated is placed in the ing with the heretofore defined water-soluble source of bath and is retained therein until the metal in the desired metal, specific ligand complexing agents. The present inthickness has been plated thereon. vention also provides a bath from which materials which The following examples illustrate a second embodiheretofore were not considered to be platable from an ment of the present invention whereby it is now poselectroless plating bath can be so plated. sible to plate such metals as cadmium, bismuth, tin, The following examples illustrate the present invention lead and zinc, although these materials heretofore were when practiced to produce a coating of nickel, iron, cobalt designated as non-catalytic materials which could not or chromium, or combinations thereof on a catalytic surbe plated electrolessly. For satisfactory plating it has face from an acid or alkaline bath. been found that the amount of chloride and/ or sulfate 10115 should be limited to an amount not in excess of EXAMPLE 1 1000 parts per million of bath by weight.

Preferred Range Nickel citrate, 2.0.1 34 16-60 gogassiuan pyrckilpholslphat 1 $0 130133 EXAMPLE 0 mm ypop osp ite g.p. 5 NQOHY m1 (1) 540 Preferred Range 1 9 0 Element; Temperature, F 140 80200 giekel ammohnitinn gliycolate, gralms litler 40 15-60 mmonium y roxi e, ercent yvo ume 15 10-20 1 20 1111 of conc. NH4OH DB! 1 10 Sodium hydroxide, gram fliter 1 0. 1-5 goiassium carbonhate, grarnsfllten i 30 10-60 0 assium pyrop osp ate, grams itcr 30 15-60 EXAMPLE 2 H Sodium hypophosphite, grams/liter 18 10-60 D 0.7 24.9-11.0 Preferred Range Temperature, F 175 12020 Cobaltous citrate, g.p.1 25 15-40 Sodium pyrophosphate, g.p.l 35 10-80 Io2nr8hypoph0sph1tag.p.l 1126103 55 2 3, -1 5 5 pH 10.5 9.0-11.0 EBAMPLE 8 Temperature, F 160 130-212 Preferred Range Element: EXAMPLE 3 Nickel iorrnate. grams liter 25 15-60 Ammonium hydroxide, percent by volume 15 10-20 Preferred Range odium hydroxide, grams/liter 1 0. 1-5 Potass um carbonate, grams/liter 30 10430 Ferrous gluconate, b.p.l 50 35-65 pot'fisslum p p l r g m 0 0-60 Sodium ascorbate, g.p.l 15 Sodium yp p sphite, gramsfhter is 10-60 D ethylam ne b0rane,g.p.l 2 1-4 DH 10,1 5 4 Glucose, g.p.l 10 350 p t F 150 120-200 Potassium citrate, g.p.l 30 10-80 pH 8.2 7.5-0.5 Temperature, F 185 150-200 EXAMPLE 0 EXAMPLE 4 Preferred Range Preferred Range Element:

Cobaltous glycolate, gramslliter 36 15-50 Chrpmous acetate, g.p.l .c 25 15-40 Potassium citrate, grarnslliter 40 20-100 Sod um erythorbate, g.p.l 25 10-60 Potassium pyrophosphate, grams/liter 30 5-60 Sodium hypophosphlte, g.p.l- 30 10-100 Sodium hydroxide, grains/liter 3 1-4 (NI-192C014, g.p.l u 30 15-60 Sodium hypophosphite, gramsyliter 30 10-50 pH 1 2.1 7.5-0.8 p11 10.2 0 3-105 Temperature, F 175 200 'lemperature, F i 150 05-150 EXAMPLE Preferred Range Element: Chromous acetate, grams/liter 20 10-25 Potassium citrate, grams/liter 30 -50 Potassium pyrophosphate, grams/liter 30 7. 5-60 Sodium erythorbate, grams/liter 15 3. 0-25 Sodium hypophosphite, grams/liter 10-50 p 9. 5 9. 1- .3 Temperature, F 150 180 EXAMPLE 11 Preferred Range Ferrous gluconate, g.p.l 50 -75 Sodium ascorbate, g.p.l 15 5-50 Dimethylamine borane, g.p.l 2 1-5 Citric acid, g.p.1 20 10-100 pH 6.0 4.5-7.0 Temperature. F 180 100-200 EXAMPLE 12 Preferred Range Nickel acetate, g.p.l 24 10-30 Sodium erythorbate, g.p.1 1. 5 0. 5-30 Morpholine borane, g.p.l 3 1-6 Ammonium hydroxide, g.p.l 5-30 pH 8.0 7. 0-10. 0 Temperature. F 100 00-200 1 10 ml. cone.

EXAMPLE 13 Preferred Range Nickel acetate, g.p.l 12 (3-25 Chromous acetate, g.p.1 12 (3-25 Potassium pyrophosphate, g.p.l 40 -80 Potassium hypopliosphite, g.p.l 50 10-100 KOH, g.p.l 5 1-30 pH 10. 1 8 0-12. 5 Temperature, F 180 160-212 Similar baths can be prepared using any of the sources of nickel, cobalt, iron and chromium defined above, alone or in combination. Further, the specific ligand complexing agent noted in each of the above baths can be replaced with any of the pyrophosphates, ascorbates or erythorbates identified herein.

The baths of the present invention provide a hard, bright, adherent plating not subject, to any substantial degree, to flaking or other deformation due to machining or fabricating of the plated material. In addition, the baths of this invention possess advantages such as greater ease and convenience of operation, operability at low temperature if desired and enhanced stability characteristics and they provide increased plating rates.

What is claimed is:

1. A bath for plating a material selected from the group consisting of bismuth, cadmium, tin, lead and zinc with a transition metal selected from the class consisting of nickel, cobalt, iron and chromium by chemical deposition consisting essentially of an aqueous solution of (a) a coordination compound of said transition metal with a saturated short chain monoor dicarboxylic acid having 1-6 carbon atoms and the hydroxy derivatives of said acids, said coordination compound of said transition metal being present in an amount ranging between 1-80 grams/liter of said bath;

(b) a ligand complexing agent selected from the class consisting of ascorbic acid, erythorbic acid, the water-soluble salts thereof and their mixtures, said ligand complexing agent being present in amounts ranging between 1-60 grams/liter of said bath;

(0) a transition metal reducing agent selected from the group consisting of hypophosphorous acid, the alkali, alkali metal and alkaline earth metal salts thereof, dimethylamine borane, morpholine borane and hydrazine sulfate, said reducing agent being present in amounts ranging between 1-100 grams/ liter; and

(d) a buffering agent in amounts sufiicient to maintain the pH of the bath from about 1-14;

said bath containing less than about 1000 p.p.m. of

anions selected from the group consisting of chloride and sulfate anions or their mixtures.

2. The bath according to claim 1 wherein the saturated short chain monocarboxylic acid is formic or acetic acid.

3. The bath according to claim 1 wherein the saturated short chain dicarboxylic acid is oxalic, malonic or succinic acid.

4. The bath according to claim 1 wherein the hydroxy derivative of said acids is glycolic, citric, lactic or gluconic acid.

5. The bath according to claim 1 which includes 7.5- grams/liter of an accelerating agent selected from the class consisting of ammonium, potassium, lithium, sodium and choline carbonates.

References Cited UNITED STATES PATENTS 3,041,198 6/1962 Certa et al. 3,096,182 7/1963 Berzins. 3,178,311 4/1965 Cann.

LORENZO B. HAYES, Primary Examiner US. Cl. X.R. 117130 Disclaimer 3,627,545.Glemz O. Mallory, J71, Inglewood, and Donald W. Bauclmnd, Temple City, Calif. BATH AND PROCESS F OR CHEMICAL METAL PLATING. Patent dated Dec. 14, 1971. Disclaimer filed Mar. 1, 1971, by the assignee, Allied Reseawoh Pmalucts, Ina. Hereby disclaims the portion of the term of the patent subsequent to Aug. 3,1988.

[O ficlal Gazette April .78, 1972.] 

